The present invention relates to a rubber fixing-roller for use in a fixing apparatus which is applied for fusing and pressing unfixed toner on a sheet so as to fix the toner onto the sheet in copier, printer, facsimile, and the like.
Heretofore, in a fixing apparatus of electrophotographic equipment, a so-called two rollers arrangement has been employed, which essentially includes two rollers, a heating roller having a heat source built-in and a pressing roller pressed to the heating roller with a predetermined pressure. In parallel with various related patent applications, this arrangement has been widely used.
In such two rollers arrangement, when it is required to provide a nip portion having a predetermined width at a position where the two rollers are rotatably contacted with each other, at least one of rollers must have a rubber elastic layer. Heretofore, the heating roller includes a rubber heat-resisting layer or fluororesin layer excellent in heat resistance because of having the heat source built-in, while the pressing roller includes a specific rubber elastic layer capable of assuring to form the nip portion.
If the rubber elastic layer of the pressing roller has a large heat capacity, the heating roller will be interfered in its temperature-rising due to the fact that the pressing roller in cool state contacts to the heating roller. As a result, a deteriorated temperature-rising rate causes a problem of long warming-up period of time. Particularly, as the heat conductivity of the rubber elastic roller is increased, this problem will come to the front, resulting in further extended warming-up period of time. Thus, it is desired to settle this problem.
In view of sufficiently providing the nip width described above, it is desirable to form the elastic layer of the pressing roller from a sponge rubber which has a high thermal responsiveness due to its low hardness or excellent elasticity, and extremely small heat capacity. This allows the rollers to be heated up to a desired fixing temperature in a short period of time. Applying this pressing roller to a fixing apparatus means to yield a capability for shortening the warming-up period of time, and is distinctly desirable from the standpoint of the recent demand for energy saving.
However, in the above case, the peripheral surface of the elastic layer in the pressing roller is heated up to the fixing temperature of, for example, about 180xc2x0 C. by receiving heat from the heating roller or heat fixing-roller. While the elastic layer formed of sponge rubber is thermally expanded inevitably by being heated up to high temperature as described above, the level of this thermal expansion is different for each region of the elastic layer depending on differences in the foamed state of sponge rubber.
The outside diameter of the pressing roller applying sponge rubber to the elastic layer is randomly varied, or irregularly deformed, in the axial direction of the pressing roller, especially just after the warming-up operation has been completed.
As a result, when an unfixed sheet supporting unfixed toner is passed through the nip portion just after the completion of the warming-up operation, the unfixed sheet tends to have corrugations due to the irregularities on the peripheral surface of the pressing roller. When such corrugations have been created in the unfixed sheet, the sheet with the corrugations loses its utility value even if a toner image can successfully fixed thereon. Taking in the broad sense, this problematically corresponds to one defect in fixing operation.
The present invention is developed to solve the problems described above. It is one object of the present invention to provide a rubber fixing-roller capable of increasing temperature-rising rate of a fixing member by limiting the rate and amount of heat-transfer from the fixing member as small as possible.
It is another object of the present invention to provide a rubber fixing-roller capable of achieving a stable fixing operation when a sheet is passed therethrough by limiting the rate and amount of heat-transfer from the fixing member as small as possible.
It is still another object of the present invention to provide a rubber fixing apparatus capable of assuring a sufficient nip width and achieving a desired low heat capacity without using sponge rubber.
It is yet another object of the present invention to provide a rubber fixing apparatus capable of assuring a sufficient nip width and having no corrugation in a sheet even just after the completion of the warming-up operation.
It is a further object of the present invention to provide a rubber fixing apparatus capable of assuring a sufficient nip width and shortening the warming-up period of time.
In order to settle the problems and to achieve the objects described above, according to a first aspect of the present invention, a rubber fixing apparatus comprises a core and an elastic layer provided on the periphery of the core, the elastic layer is adapted to satisfy the following formula;
0.0004xe2x89xa6Axe2x89xa60.0037
where A (J2/secxc2x7cm4xc2x7K2) is a product value from the specific heat (J/gxc2x7K), density (g/cm3), and heat conductivity (W/mxc2x7K) of said elastic layer
In the rubber fixing-roller according to the first aspect of the present invention, the peripheral surface of the elastic layer may be covered with a releasing layer. This releasing layer may be formed of fluororesin.
In the rubber fixing-roller according to the first aspect of the present invention, the elastic layer may include a material having low specific heat and low heat conductivity dispersed in the elastic layer. This elastic layer may be formed of cellular rubber, preferably foamed rubber.
Alternatively, the elastic layer may be formed of a rubber with which a hollow filler, preferably a glass balloon, is dispersedly mixed as the material having low specific heat and low heat conductivity. The elastic layer may otherwise be formed of silicon rubber.
In the rubber fixing-roller according to the first aspect of the present invention, the rubber fixing-roller may be positioned to contact to the fixing member with a predetermined pressure.
According to a second aspect of the present invention, a rubber fixing-roller comprises a core and a non-foamed rubber elastic layer provided on the periphery of the core, the layer including a peripheral surface having a predetermined outside diameter, the layer being prepared in a predetermined heat capacity per unit volume by mixing a filler having low density and low specific heat.
In the rubber fixing-roller according to the second aspect of the present invention, the peripheral surface of the elastic layer may be covered with a releasing layer. This releasing layer may be formed of fluororesin.
In the rubber fixing-roller according to the second aspect of the present invention, the filler having low density and low specific heat may be a hollow material, or otherwise include a multi-component glass.
In the rubber fixing-roller according to the second aspect of the present invention, the rubber fixing-roller may be adapted to satisfy the following formula;
0.77xe2x89xa6xcfx81xc2x7 cxe2x89xa61.32
where xcfx81 is a density (g/cm3) and c is a specific heat (J/gxc2x7K), in the range of from the peripheral surface of the elastic layer to at least 2 mm in depth.
In this case, the filler having low density and low specific heat is preferably not mixed in the range deeper than 2 mm in depth from the peripheral surface of the elastic layer.
In the rubber fixing-roller according to the second aspect of the present invention, the rubber fixing-roller may be adapted to satisfy the following formula;
xe2x80x830.77xe2x89xa6xcfx81xc2x7 cxe2x89xa61.32
where xcfx81 is a density (g/cm3) and c is a specific heat (J/gxc2x7K), in the entire range of the elastic layer.
These and other aspects of the present invention are apparent in the following detailed description and claims, particularly when considered in conjunction with the accompanying drawings.